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linear predictor function : ウィキペディア英語版
linear predictor function

In statistics and in machine learning, a linear predictor function is a linear function (linear combination) of a set of coefficients and explanatory variables (independent variables), whose value is used to predict the outcome of a dependent variable. Functions of this sort are standard in linear regression, where the coefficients are termed regression coefficients. However, they also occur in various types of linear classifiers (e.g. logistic regression, perceptrons, support vector machines, and linear discriminant analysis), as well as in various other models, such as principal component analysis and factor analysis. In many of these models, the coefficients are referred to as "weights".
==Basic form==
The basic form of a linear predictor function f(i) for data point ''i'' (consisting of ''p'' explanatory variables), for ''i'' = 1, ..., ''n'', is
: f(i) = \beta_0 + \beta_1 x_ + \cdots + \beta_p x_,
where \beta_0, \ldots, \beta_p are the coefficients (regression coefficients, weights, etc.) indicating the relative effect of a particular explanatory variable on the outcome.
It is common to write the predictor function in a more compact form as follows:
*The coefficients ''β''0, ''β''1, ..., ''β''''p'' are grouped into a single vector ''β'' of size ''p'' + 1.
*For each data point ''i'', an additional explanatory pseudo-variable ''x''''i''0 is added, with a fixed value of 1, corresponding to the intercept coefficient ''β''0.
*The resulting explanatory variables ''x''''i0'', ''x''''i''1, ..., ''x''''ip'' are then grouped into a single vector ''xi'' of size ''p'' + 1.
This makes it possible to write the linear predictor function as follows:
:f(i)= \boldsymbol\beta \cdot \mathbf_i
using the notation for a dot product between two vectors.
An equivalent form using matrix notation is as follows:
:f(i)= \boldsymbol\beta^ \mathbf_i = \mathbf^_i \boldsymbol\beta
where \boldsymbol\beta and \mathbf_i are assumed to be a ''p''-by-1 column vectors (as is standard when representing vectors as matrices), \boldsymbol\beta^ indicates the matrix transpose of \boldsymbol\beta (which turns it into a 1-by-''p'' row vector), and \boldsymbol\beta^ \mathbf_i indicates matrix multiplication between the 1-by-''p'' row vector and the ''p''-by-1 column vector, producing a 1-by-1 matrix that is taken to be a scalar.
An example of the usage of such a linear predictor function is in linear regression, where each data point is associated with a continuous outcome ''y''''i'', and the relationship written
:y_i = f(i) + \varepsilon_i = \boldsymbol\beta^\mathbf_i\ + \varepsilon_i,
where \varepsilon_i is a ''disturbance term'' or ''error variable'' — an unobserved random variable that adds noise to the linear relationship between the dependent variable and predictor function.

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
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